1. Technical Field
The exemplary embodiments of the present invention relates to a semiconductor device, and more particularly, to a resistive memory device and a fabrication method thereof.
2. Related Art
As typical next-generation memories which replace dynamic random access memories (DRAMs) or flash memories, there are resistive memory devices. The resistive memory devices are memory devices using a variable resistive material which switches at least between two different resistance states by rapidly changing its resistance in response to an applied voltage.
As an example of the resistive memories, there are phase-change random access memories (PCRAMs). The PCRAM generally includes a switching element, a lower electrode formed on the switching element, a phase-change material pattern formed on the lower electrode, and an upper electrode formed on the phase-change material pattern.
As a phase-change material mainly used in the PCRAMs, there is Germanium-antimony-tellurium (Ge—Sb—Te, GST). A melting point of GST is about 630° C. and GST transitions from an amorphous state into a crystalline state at a crystallization temperature which is about 150° C.
A diode is mainly used as the switching element of the PCRAM and a method of forming a diode is accompanied by a high temperature process of 1000° C. or more.
In general, in a single-layered PCRAM, the diode is formed and then the phase-change material layer is formed so that high heat applied in the fabrication process of the diode does not affect the phase-change material.
With demands on high integration of semiconductor devices, memory cells with a multi-layered stack (MLS) structure are being fabricated. In the PCRAM cell having the MLS structure, two or more stages of cells are stacked, that is, an upper stage cell (including a diode/a lower electrode/a phase-change material pattern) is formed on a structure in which a lower stage cell (including a diode/a lower electrode/a phase-change material pattern) is formed.
Since a process of forming the diode for the upper stage cell is accompanied by a high temperature process, a thermal attack may occur in the phase-change material pattern, which has been already formed in the lower stage cell.
Therefore, a method of forming a diode using a laser annealing process has been considered. The laser annealing process for forming the diode may be performed at a temperature of 1000° C. for a short time of 0.5 ms and thus protect the phase-change material pattern of the lower stage cell by shortening a high-temperature application time.
However, even when the annealing process using laser is applied to form the diode, the effect on the phase-change material pattern of the lower stage cell may still exist and thus it may be difficult to ensure desired fabrication yield and operation reliability for the fabricated memory cell.